Prior art selective call message handling systems generally accumulated messages at a central station also referred to as a paging terminal, and transmitted the messages to a selected group of selective call receivers also referred to as pagers. Such a system may use the Golay Sequential Code (GSC) which is well known to those familiar with the art. The operation of the GSC system has been described in detail in U.S. Pat. No. 4,424,514 to Fennell et al. entitled "Decoder for Transmitted Message Activation Code" and U.S. Pat. No. 4,427,980 to Fennell et al. entitled "Encoder for Transmitted Message Activation Code".
A brief description of the tone only, numeric, and alphanumeric messaging aspects of GSC is presented herein. The paging terminal accumulates messages for a group of pagers. The messages are then structured into a GSC packet and transmitted.
FIG. 1 shows the prior art packet structure 20 of the Golay sequential system. A packet has a preamble 22 followed an at least one batch 24 of information. Preamble 22 has a 1.4266 second duration. The preamble format starts with 28 bits of comma 26 at 600 bits per second (bps) followed by eighteen transmission of a preamble word 28. Comma is an alternating 1-0 pattern. A preamble word 28 is a 23,12 BCH code and is transmitted at 300 bps. The eighteen preamble words are identical and are a predetermined code word used for selecting a group of pagers.
The preamble is followed by at least one batch 24 of signals, each batch starts with a sync code 30 and is followed by 16 slots 32 of information. A batch transmission has a 3.42833 second duration. The sync code 30 at the beginning of the batch has a 0.20166 second duration. The sync code 30 starts with 28 bits of comma 34 at 600 bps and is followed by a predetermined 23,12 code word 36 at 300 bps which is followed by one comma bit 38 at 600 bps, and ends with a second predetermined 23,12 word 40 at 300 bps. The sync code 30 indicates the start of a batch.
The 16 slots 32 which follow the sync code may have address or activation codes 42 or may have information 52. When a slot has an address or activation code, the format of the slot is similar to the format of the sync code 30 wherein the slot begins with 28 bits of comma 44 at 600 bps, followed by a 23,12 word 46 at 300 bps, followed by one comma bit 48 at 600 bps, and then followed by a second 23,12 268 word at 300 bps. Note that addresses and the activation code are similar in structure both having two 23,12 words. For the activation code, the two 23,12 words 46 and 50 are predetermined. For addresses, the two 23,12 words 46 and 50 may be one of a plurality of words allowing for a multitude of addresses. During an address decode, the pager searches for a match of both the first word 46 and the second word 50 with a unique first and second word assigned to a pager.
A slot may also have data information 52, a data information slot starts with a comma bit 272 transmitted at 600 bps, followed by eight 15,7 words 54 and 56 transmitted at 600 bps. A 15,7 word is a coded word having 15 total bits of which 7 bits are information bits. The remaining 6 bits are parity based upon the 7 information words and may be used for error detection or correction. The eight 15,7 words are structured into seven information words 54 followed by a check word 56. The seven information words 54 form a block of 49 information bits. A block of information is structured to have 48 bits used for pager information and the 49th bit is used as a continue bit. The continue bit indicates that the subsequent slot has additional information.
In a typical application, a preamble is followed by at least one batch, a batch beginning with a sync code and followed by 16 slots. If a slot has a tone only address or group information, the subsequent slot may have an address or additional group information. If a slot has a numeric or alphanumeric address, the subsequent slot has data information associated with the address. The tone only address or the combination of a numeric or alphanumeric address with data comprises a message for a pager.
FIG. 2 shows a prior art paging terminal operation. The prior art paging terminal's first function is to accumulate messages for a group of pagers, step 60. The messages are then packaged into slots, step 62, either address or information or activation codes, the packaging being detailed in FIG. 1. Batches are then created by inserting a sync code in every 17th slot, step 64. A packet is then created by adding a preamble particular to a group of pagers at the beginning, step 66. The packet is then transmitted in step 68.
FIG. 3 refers to prior art battery saving operation for a single batch packet, the packet being created by a paging terminal operating in accordance with the prior art flow chart of FIG. 2. Line 70 indicates the signal which is transmitted by the base station and received by the selective call receiver. The shaded area indicates that nothing is transmitted by the paging terminal and noise is received by the pager. The packet begins with a preamble signal labelled PREAMBLE followed by a sync code which is illustrated by the letters SC in a box. After the sync code, 16 boxes corresponding to the 16 slots of FIG. 1. Inside each of the boxes is a letter A, D, or X. The letter A corresponds to an address for a selective call receiver. The letter D corresponds to data, the data being associated with a preceding address and the address and data making up a message for a selective receiver. The letter X corresponds to a slot which has no message information. X may be transmitted when a portion of the packet information is complete and no additional information is left to transmit to the selective call receivers. X may be an idle code address reserved for filling the remainder of a batch.
Line 72 indicates the battery saver operation of the prior art pager during signal 70. Beginning at event A, line 70 shows a shaded area which corresponds to noise indicating no transmission. In the noise environment line 72, events B and C show the pager being periodically activated during the search for a preamble. The pager is active while line 72 is high and battery saving while line 72 is low. An active pager indicates a pager that is consuming electrical energy. In the active state, the receiver is powered on and demodulating the transmitted signal while the decoder is analyzing and processing the demodulated signal. In the battery saving mode, the receiver and decoder operate in a reduced power mode.
For events B and C, the pager is active long enough to detect at least one preamble word. In the event a preamble word is not detected, the pager returns to battery saver mode.
At event D, the base station begins a packet transmission. The packet transmission begins with a preamble. At event E, the pager is active and finds a preamble word. Upon finding a preamble word, a search for a sync code begins. Sync is found at event F. Upon finding sync code, the batch decoding begins. Decoding of the batch, event H, is well known to those familiar with the art. At event L, the batch is terminated and the RF signal is again noise as indicated by the shaded area of line 70. During event L, the pager searches for a subsequent sync code which, if received, indicates a subsequent batch will be transmitted. Upon finding no sync code, the pager reverts to a preamble search battery saver operation.
Note that the prior art pager is active for the entire duration of the packet. Typically, an address search is performed during slots when addresses or data is transmitted and during slots when idle code may be transmitted as indicated by the letter X. The prior art pager terminates the packet upon searching for a sync code. The presence of a sync code indicates the start of a subsequent batch in the packet and the absence of a sync code indicates the end of the batch. Upon detecting the absence of the sync code, the pager reverts back to a preamble search mode.
The packet indicated in FIG. 3 has four tone only messages and two numeric or alphanumeric messages. A slot with an address followed by a slot comprising another address or an idle code word can indicate a tone only address. The two messages with numeric or alphanumeric type data are indicated by addresses followed by subsequent data slots. In each case, there is an address followed by three data blocks which corresponds to a message for a selective call receiver. A prior art pager that has not detected its own address decodes a data slot as an address. The data slot is structured in such a manner so as to inhibit the detection of an address during a data slot transmission. However, the pager searching for an address while data is being transmitted unnecessarily expends electrical energy during the search for an address.
FIG. 4 is a flow chart showing the operation of a prior art pager. Prior art pager battery saver operation is shown in FIG. 3. The operations may be executed by a program operating within a paging decoder. The program starts at step 102 wherein power on initialization functions are performed. Such functions are well known to those familiar with the art. The program proceeds to step 104 to activate the receiver during which time the receiver is powered on and transmitted signals are demodulated and processed. The program proceeds to step 106 to search for preamble for about 0.15 seconds. During this time, the receiver is activated for about 0.15 seconds and the decoder activate searches for a preamble signal. If preamble is not found, the pager proceeds to step 108 to turn the receiver off and to perform battery saving for about 1.30 seconds. After completion of step 108, the program returns back to step 104 to turn the receiver on. Steps 104-108 incorporate the steps performed during the preamble search operation of the pager.
If in step 106 the preamble was found, the program proceeds to step 110 to check for a sync code. The sync code is searched for about 1.45 seconds. If sync code is not found within about 1.45 seconds, the program returns to step 108 to turn the receiver off and then to reenter the preamble search mode. If in step 110 a sync code is found, the program proceeds to step 128 to initialize for the first slot in a batch. The pager then decodes the slot in step 122.
The program proceeds to step 118 to check if a pager address is found. If in step 118 a pager's address is not found, the program proceeds to check if 16 slots have elapsed, step 120. If 16 slots have not elapsed, the program returns to step 122 to decode the next slot. Steps 118, 120, and 122 are performed for the 16 slots within a batch. Upon the end of the 16th slot, step 120 proceeds to step 124 to decode the next slot and then in step 126 to check for a sync code. If a sync code is found, a subsequent batch is appended to the packet and the program returns to step 128 to reinitialize for the first slot in the subsequent batch. After completion of step 128, the program proceeds through steps 118-122 to decode the information within the subsequent batch. If in step 126 the sync code is not found, the program returns to step 108 to turn the receiver off and to begin the preamble search.
Referring back to step 118, if a pager address is found, the program checks if the address is alphanumeric or a tone only. The response to a tone only address is well known to those familiar with the art and is not detailed in this flow chart. However, upon reception of a tone only address, the pager invokes a tone only alert function and then proceeds to step 120 to continue searching for addresses. If the address in step 618 is an alphanumeric or numeric address, the program proceeds to step 130 to check if 16 slots have elapsed. If 16 slots have not elapsed, the program proceeds to step 132 to decode the next slot and handle the message within. The program then proceeds to step 134 to check if two consecutive slots were in error. The slot error determination is made by testing, in a manner known to those familiar using the art, the check sum word 56 of FIG. 1 with the information words 54 of FIG. 1. If the test is successful, the slot is not in error, otherwise the slot is errored. If two consecutive slots are not in error, the program proceeds to step 136 to check for the end of the message. The end of a message is indicated by a predetermined character within an information word. If the message has not been ended, the program returns to step 130 to check if 16 slots have elapsed. The elapsing of 16 slots indicates the completion of a batch. Upon the completion of a batch, the program proceeds to step 138 to decode the sync code next slot. If the sync code was found, the packet has a subsequent batch and the program proceeds to step 142 to initialize for the first slot in the batch. The program returns to the message decoding of step 132. However, if the sync code was not found, the slot is flagged as an errored slot, and the evaluation will be considered in step 134. The program then proceeds to step 142.
In the event the user of the pager travels into an area where the RF signal grows weak, the information slots within the message may become corrupted by noise. ,If there are two consecutive slots corrupt within the message, step 134 returns to step 108 to being a preamble search. On the other hand, if all of the data associated with the message is decoded, an end-of-message character is encountered. Upon encountering an end-of-message character, step 136 returns the program to step 120 which puts the pager back into an address decoding mode.
In portable selective call receivers, it is desirable to achieve a maximum battery life. A way to achieve improved battery life is to prohibit a pager from expending electrical energy searching for an address while data is being transmitted within a packet. Thus, it is desirable to transmit packet structure information within the packet indicating the locations of addresses as well as other group information within the packet. Group information, which is also referred to as other information, is information to be received by a plurality of selective call receivers and includes activation codes and packet structure information. Pagers may then use the packet structure information to expend electrical energy searching for their address or group information only at the time of an address or group information transmission and perform battery saving at the time of subsequent data transmissions, unless, of course, the data is transmitted to a particular selective call receiver.
It is desirable to implement a pager being compatible with the existing GSC transmission technique, allowing the addition of the structure information within the packet to be transmitted and decoded by pagers capable of interpreting the structure information without interfering with the operation of prior art GSC pagers not capable of interpreting the structure information. It is also desirable for the pagers to be capable of decoding and handling the new structure information to operate on existing GSC paging terminals that do not transmit structure information within the message packet. In such a case, the improved battery saver detailed by the present invention would not be realized.
It is also desirable to have a paging terminal capable of accumulating messages into a packet. The paging terminal then determines the location of addresses and group information within the packet, generates the packet structure information and inserts the packet structure information within the packet. The paging terminal then transmits the packet to the pagers.